Tube coils



NOV- 3, 1942 D. M. scHoENFr-:LD

TUBE COILS Filed April 26,` 1941 5 Sheets-Sheet l bh. Nm.

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l HUI NOV 3, 1942. D. M. scHoENFELD TUBE COILs Filed April 26, 1941 3 Sheets-Sheet 2 INVENTOR Zal/ae 1% Jr/mm/d BY K ORNEY NOV. 3, 1942- D. M. scHoENFELD l 2,300,534

TUBE COILS Filed April 26, 1941 3 Sheets- Sheet 3 INVENTOR gjm* [I al//d Mam/ela BY comes excessive.

Patented Nov. 3, 1942 o, TUBE cons s Davia M. schoenfem, New Yara-MY., assigner' to Combustion Engineering Company,

-Inc.,y New Applicatinnprii 26,1941, serial 1515.390532 s claims. (c1. 122-250) This invention relates to improvements in tubular heat exchange elements adaptedj for use in forced circulation-,boilers and particularly in waste heat forced circulation boilers.

In waste heat boilers such as those used to extract heat from exhaust gases of gas engines, it is desirable to have the tubes arranged compactly so as to occupy a small space. A flat tube coil is a useful form of heat exchange element for constructing such aboiler. ly made by bending a continuous tube in a plane into a spiral between the circumference and the center and a plurality of such coils are arranged one upon another, the ends being connected into inlet and outlet headers for receiving and discharging the fluid to be heated. The assembled coils are usually mounted inacylindrical c-asing which is suitable for resisting internal gas pressures. When these superimposed coils are all made-alike, the lengths and diameters of tubes being equal, the resistancev to fluid flow therethrough varies considerably; the coils through which all liquid or nearly all liquid flows have a much lower pressure drop from end to end than those coils through which a major portion of vapor flows in the vapor liquid mixture. This relatively high resistance of the coils in which vapor predominates may cause a greater pressure drop therethrough than is warranted or can be economically met by the design since the power required to operate the circulation pump be- To overcome this difficulty the coils, when made of tubing of the same tube diameter, may be varied in length, the coils in which vapor predominates being made relatively shorter than the coils in which the liquid predominates.

It is an object of this invention to provide in a forced feed vapor generator a plurality of spirally wound coils through which the fluid to be vaporized is forced in parallel circuits, the coils being divided into sets arranged in superimposed relation. The coils in one set are of different lengths than the coils in another set and so arranged that each of the assembled sets has substantially the same overall diameter and tube length, the same tube size and tube spacing in all groups, whereby the resistance to fluid flow through each of the coils is substantially the same.

How the foregoing, together with other objects and advantages as may hereinafter appear or are incident to my invention are realized, is illustrated in preferred form in the accompanying drawings wherein:

These coils are usual- Figure 1 is an elevational view, partly in section, of a waste heat type boiler embodying tubular heat exchange elements formed in accordance with the present invention;

Figures 2 and 3 are plan views each illustratingy one of the two coils forming the set illustrated in Figure 4.

Figure 4 is va sectional view on an enlarged scale through a set of elements utilized in the upper part of the boiler, the set consisting of two superposed tube` coils having' tube turns arranged in staggered-relation;

Figure is a plan view onv an enlarged scale of one of the. sets of tube coils utilized-inthe lower portion ofthe boiler, the setconsisting of three tube coils; f

Figure 6 isa sectional view on line 6,-6 in Figure 5 `and illustrates the relationship of the three coils forming the set shown in Fig. 5.

Figures 7 and 8V are plan viewsof two'of the coils forming the set illustrated in Figs. 5 and 6;

F'gure 9 is a plan view of the thirdl coil-in the set illustratedin Fig. 5.

.Referring Ito Fig. 1, the heat absorbing surface of the boiler consists of tube coils Vdivided Ainto two groups designated asv Ill and I I and mounted in a cylindrical casing |21v When the boiler utilizes `waste heat, vthev ends of casing I2 are vsuitably.contractedf'at I4 for connectionvto a hot gas conduit at the'bottom and at I5 for connection to an oiftake flue I5. vAn inlet header It and an outlet header I1 are located exteriorly of the cylindrical casing I2 and are so connected to the tube coils as to supply the liquid to be vaporized to the coils and remove the vapor-liquid mixture therefrom.

In the embodiment shown in Fig. 1, the sets of coils in the boiler are divided into two groups, designated I0 and II. Group I0 is farthest removed from the inlet for hot gases and relatively little steam is made in its tubes. It consists of sets of coils arranged as shown in Figs. 2, 3 and 4. Group II which is nearest to the hot entering gases and in `which a major portion of the tubes are filled with steam, is constructed of sets of coils as shown in Figs. 5 to 9.

Figs. 3 and 4 show, respectively, the top and bottom tube coils making up one of the several sets of elements in group I0. Each set is made up of two superimposed tube coils 24 and 25. Liquid enters each coil through the ends 26 and 2'I which connect with headers I6 and I1 respectively. The coils 24 and 25 are wound spirally on slightly spaced axes so that when assembled in superimposed relation as shown in Fig. 4, the

Il. The tubes in lcoils 30 and 3| have convo1u-.

tions wound to form at ring coils, 'so that when assembled in superimposed relation as shown in Figs. 5 and 6 the tubes of ,therbottom coil'SQlare f staggered with respect to vthegtubesvof` theftop coil 3l. When the tube 'coils 30 and 31 are assembled there is a central opening in the .set which is filled in by the tube coil 32 Vshown in plan' in Eig. 9i Tube coi'l 32 differs from theremaining coils in that the continuous tube from which it is made is wound in two superimposed flat volute coils, one spiralling toward the center'and the other toward the circumference, each volute coil being located in a plane with one of the tube coils =30 and 3| of'the assembled set. The tubes of the voluteof the upper part of coil 32 are staggered with respect to the tubes of the volute of the lower coil. l

'I'he two tube coils 24 and 25 forming a set in group IU have substantially the same total tube length as the three tube coils 30, 3l and 32 forming a set in group I I, one tube coil 24 or 25 being one and one-half times as long as the length of one tube coil30, 3l or 32. -Since' the Velocity of fluid flow through the tubes of groupl l is greater than that through the tubes of group l0, the resulting greater resistances per u nit length of the latter are offset by' their shorter length 'of'tubes and a closer uniformity of pressure drop for the groups is obtained.

What I clamis: I

l. In a heat exchanger having a chamber provided with an inlet and outlet for circulating a heating gas therethrough; a plurality of heat absorbing units mounted in said chamber near the outlet thereto each lcomprising a tubularelement wound in a plurality of' closelyspaced convolutions to 'form a at volute coil disposed transversely of said chamber; aplurality of heat absorbing units mounted in said .chamber neary the inlet thereof each comprising a tubular element wound in a plurality of -closely spaced convolutions to form a flat ring coil disposed transversely of vsaid flue; a plurality of tubular elements each wound in a plurality of closely spaced convolutions to form a double ilat volute coil fitting within and concentric with two of said ring coils, one volute section being in the plane of one ring coil and the other volute `section being in the plane of an immediately adjacent ring coil, the aggregate length of the tubular elements form- Ying two ring coils and a related double volute coil being substantially the same as the length of two tubular element-s formingr a volute coil disposed near the-outlet of said chamber and the dia-meters of all 'said tubular elements being the same; and inlet and outlet headers to which opposite ends of the tubular elements forming each coil are connected.

2. In a heat exchanger having a gas duct, and inlet and outlet headers for a fluid to be heated; a pair ofV heat absorbing coils located in said duct comprising tubular elements connected at 0pposite ends to said inlet and outlet headers and wound in a plurality of closely spaced convolutions about the longitudinal axes of said duct to form flat ring coils located in planes transverse of said duct, Vsaid twocoils being located in immediately adjacent planes; and a tubular element wound spirally in one direction in spaced convolutions to form `a at volute coil disposed in the plane of one ring .coil and wound specially in the opposite direction in closely spaced convolutions to form another flat volute coil located in the plane of a second immediately adjacent ring coil. f

3. iIn a heat `exchanger' having a gas duct, and inlet and outlet headers for a fluid to be heated disposed longitudinally of said duct; a plurality or flat heat absorbing coils each constructed of the same size of tube disposed in parallel planes transverse of said duct and individually connected to said inlet and outlet headers, the length of a heat yabsorbing coil located in a heat zone near the inlet of said duct being less than the length of a coil located in aicoolerzone near the outlet of said duct in approximate inverse proportion to the respective resistances to fluid flow therethrough per unit of length.

' DAVID M. SCHOENFELD. 

